The prevention, removal, and remediation of hydrogen sulfide (H2S) and other sulfhydryl compounds from liquid or gaseous industrial process streams is a challenge in a wide range of industries. The presence of H2S poses significant environmental and safety concerns to personnel and operators. This is due in part to the fact that H2S is highly flammable, highly toxic when inhaled (8 h of exposure at 100 ppm has been reported to cause death while levels of 1,000 ppm can cause death within minutes), highly corrosive, and malodorous. Further, corrosion and scale deposits resulting from the presence of hydrogen sulfide in contact with metallic surfaces, such as carbon steel pipes can further disruption industrial operations via the plugging of pipes, valves, nozzles, and the like.
In the oil and gas industry, the removal of H2S is important for the transport and storage of crude reserves as well as meeting standards for downstream refining, an important consideration due to sulfide poisoning of cracking catalysts and transmission of gas. Further, in both the refining industry and geothermal power industry, cooling tower process water can contain moderate to high levels of H2S, both causing significant solids development as well as increasing the level of oxidant demand so as to make oxidants unviable options for microbial control in these systems.
Nonetheless, the challenge of removing and/or reducing H2S from process streams has been addressed with a variety of different technologies. Common techniques utilize either absorption with a solvent or solid phase material with subsequent regeneration of the absorbent, or reaction with a suitable substance or substrate that produces a corresponding reaction product. This reactivity has often involved the reaction of H2S with various types of aldehydes. For instance, U.S. Pat. No. 1,991,765 was an early example describing the reaction of formaldehyde with hydrogen sulfide to form an insoluble product, later identified as the sulfur heterocycle 1,3,5-trithiane.
U.S. Pat. No. 2,426,318 discloses a method of inhibiting the corrosivity of natural gas and oil containing soluble sulfides by utilizing an aldehyde such as formaldehyde.
U.S. Pat. No. 3,459,852 discloses a method for removing sulfide compounds with α,β-unsaturated aldehydes or ketones such as acrolein or 3-buten-2-one as the reactive compounds. Nonetheless, acrolein is a hazardous, highly toxic chemical limiting extensive use in a wider variety of applications.
U.S. Pat. No. 4,680,127 describes a method for reducing H2S in a neutral to alkaline aqueous medium (pH ˜7-9) with the formation of solids, a problem when using formaldehyde, using glyoxal and glyoxal/formaldehyde mixtures without the formation of solids. However, the glyoxal/formaldehyde mixtures exhibited slower rates of H2S scavenging than glyoxal alone.
European patent application EP 1 624 089 A1 describes the use of mixtures of glyoxal with a metal nitrate compound in conjunction with triazines or N-chlorosuccinimide for preventing H2S odor generation, particularly that being microbial in origin, but not being biocidal. This reduction in H2S was reported to reduce corrosion as well. The use of the N-chlorosuccinimide was for the purpose of maintaining a particular redox potential and intended to oxidize or consume residual H2S. Maintenance of a halogen residual after H2S scavenging is not described.
U.S. Pat. No. 4,978,512 describes a method whereby an alkanolamine and an aldehyde are combined to form a triazine in order to scavenge H2S.
U.S. Pat. No. 5,498,707 describes a composition wherein a diamine and an aldehyde donor are utilized to scavenge H2S from liquid or gaseous process streams.
The composition forms water soluble polymers but does not claim to impact iron sulfide scale.
U.S. Pat. No. 7,438,877 discloses a method for H2S removal utilizing mixed triazine derivatives for improved scavenging. The mixture improves the overall scavenging capacity of triazines, but whether complete removal is achieved for a theoretically stoichiometric amount is not reported. However, it is known that typically triazines, such as hydroxyethyl triazines, do not scavenge H2S stoichiometrically (i.e., 3 mol of H2S per mol triazine) due to formation of cyclic thiazines that do not further react with H2S (Buhaug, J.; Bakke, J. M. “Chemical Investigations of Hydroxyethyl-triazine and Potential New Scavengers”, AIChE 2002 Spring National Meeting).
In addition, methods and compositions have been described for the treatment of iron sulfide deposits. For instance, U.S. Pat. No. 6,986,358 discloses a method for combining an amine with tris(hydroxymethyl)phosphine in a reaction at a pH of 8 to complex and dissolve deposits of iron sulfide. Similarly, the combination of ammonia with bis-(tetrakis(hydroxymethyl)phosphonium) sulfate forms a tetradentate ligand that complexes iron (Jeffrey, J. C.; Odell, B.; Stevens, N.; Talbot, R. E. “Self Assembly of a Novel Water Soluble Iron(II) Macrocyclic Phosphine Complex from Tetrakis(hydroxymethyl)phosphonium Sulfate and Iron(II) Ammonium Sulfate”: Chem. Commun., 2000, 101-102. Further, WO 02/08127 A1 combines the concept of using an amine, carboxylic acid amine salt, aminophosphonic acid, or ammonia in combination with bis-(tetrakis(hydroxymethyl)phosphonium) sulfate or tris(hydroxymethyl)phosphine to inhibit and reduce the amount of iron sulfide deposits in a water system.
While multiple methods have been developed for scavenging H2S and sulfhydryl compounds from industrial process systems, a high capacity, fast reacting method for reducing hydrogen sulfide, mitigating sources of hydrogen sulfide, such as microbiological sources, and removing products of hydrogen sulfide corrosion, such as iron sulfide, which performs at similar levels over a wide pH range and does reduces solids formation is still desired. Further, it is desirable to be able to use the chemical in industrial process systems that have H2S present via either process leaks or influent, such as produced water storage tanks, fracturing fluids, cooling tower refineries, and geothermal cooling towers.